1. Field of the Invention
The present invention relates to an electrostatic capacitor-type inclination sensor, with a pair of differential electrodes and a common electrode arranged facing each other within an air-tight container, for detecting changes in the fluid surface level of dielectric fluid introduced into the air-tight container as changes in electrostatic capacitance corresponding to an angle of inclination. More particularly, the present invention relates to an electrostatic capacitor-type inclination sensor that does not require temperature compensation or zero adjustment.
2. Description of Related Art
It is known to provide an inclination sensor mounted on a vehicle such as a motorcycle to detect the inclination of the vehicle and control various parts of the vehicle in response thereto. FIG. 15 is a perspective view of a related art motorcycle mounted with an inclination sensor, viewed from the rear. The inclination sensor 90 attached to, for example, a stay etc. extends forward from the handlebar stem at the front end of a main frame (not shown). The inclination sensor 90 inclines integrally with the main frame, i.e. the vehicle body, regardless of where the helm of handlebars 92 is. The inclination angle is then detected and this angle is detected. An angle signal detected in this manner is then sent to an ECM (engine control module) fixed, for example, to the lower part of a seat 91 towards the rear of the vehicle and is utilized in various control.
Related electrostatic capacitor-type inclination sensors are disclosed in, for example, Japanese Patent Laid-open Publication Nos. Hei. 4-53528 and Hei. 5-14168. FIG. 7 is a vertical cross-section of a related art electrostatic capacitor-type inclination sensor, FIG. 8 is a lateral cross-section, and FIG. 9 is a perspective view of a variable capacitor section.
In the variable capacitor section, a pair of differential electrodes 11a and 11b are arranged next to each other in a horizontal direction and a common electrode plate 12 is provided parallel with the differential electrodes 11a and 11b, with a fixed gap remaining between the differential electrodes 11a and 11b and the common electrode plate 12. The differential electrodes 11a and 11b and the common electrode plate 12 are housed in an airtight container 14. The airtight container 14 is filled up to approximately half its effective capacity with a dielectric fluid 13 such as silicon oil. Each of the differential electrodes 11a and 11b and the common electrode plate 12 form variable capacitors Ca and Cb.
FIG. 10 shows an example of a circuit for converting changes in capacitance of the variable capacitors Ca and Cb into changes in d.c. voltage for a related electrostatic capacitor-type inclination sensor, with an oscillator OSC being connected to the common electrode plate 12. Each of the differential electrodes 11a and 11b are connected to capacitance/voltage conversion circuits CV1 and CV2 for converting changes in capacitance to changes in d.c. voltage. Each of the differential electrodes 11a and 11b are connected to capacitance/voltage conversion circuits CV1 and CV2 for converting changes in capacitance into changes in d.c. voltage. Output signals of the capacitance/voltage conversion circuits CV1 and CV2 are inputted to a differential amplifier DA and the output of this differential amplifier DA is a d.c. signal corresponding to the angle of inclination of the sensor.
A zero-point adjustment circuit 81 controls the capacitance/voltage conversion circuit CV2 in such a manner that the output voltage of the differential amplifier DA becomes 0V when the sensor is horizontal. A temperature compensation circuit 82 controls the amplification factor of the differential amplifier DA according to the atmospheric temperature in such a manner that an output corresponding to the angle of inclination of the sensor is obtained regardless of the temperature.
FIG. 11 is a view showing the relationship between electrostatic capacitances Ca and Cb of the variable capacitors Ca and Cb (in the following, the electrostatic capacitors of the variable capacitors are expressed as the numerals given to the variable capacitors) and the angle of inclination of the sensor, with this relationship being shown as changes of temperature and individual differences within a range shown by broken lines.
On the other hand, in the related technology, the output of the differential amplifier DA representing the angle of inclination of the sensor is a function of the difference of the electrostatic capacitances of the variable capacitors Ca and Cb. When the electrostatic capacitances of the variable capacitors C1 and C2 change according to temperature and individual differences, the difference between the electrostatic capacitances (Caxe2x88x92Cb) also changes within the range of the broken lines as shown in FIG. 12.
In the above related technology, at least one of the capacitance/voltage conversion circuits CV1 and CV2 has to be zero point-adjusted by the zero-point adjustment circuit 81 for each sensor so that the output of the differential amplifier DA becomes xe2x80x9c0xe2x80x9d when the difference is xe2x80x9c0.xe2x80x9d It is also necessary to carry out temperature compensation for each sensor at the temperature compensation circuit 82. However, particularly when the sensor is mounted on a vehicle such as a motorcycle, in addition to it not being easy to accurately perform zero point adjustment and temperature compensation when the vehicle is in motion, there are also increases in cost and weight.
In order to resolve the aforementioned problems, it is the object of the present invention to provide a low-cost electrostatic capacitor-type inclination sensor where regulators such as zero-point adjusters and temperature compensators etc. are not required. In order to achieve the aforementioned object, the present invention includes the following:
(1) In an electrostatic capacitor-type inclination sensor, with a pair of differential electrodes and a common electrode arranged facing each other within an air-tight container, for detecting changes in the fluid surface level of dielectric fluid introduced into the air-tight container as changes in electrostatic capacitance corresponding to an angle of inclination, the pair of differential electrodes are arranged next to each other in a vertical direction with respect to the fluid surface level when the fluid surface level is horizontal.
(2) An electrostatic capacitor-type inclination sensor with a pair of adjacent differential electrodes and a common electrode arranged facing each other within an air-tight container, for detecting changes in the fluid surface level of dielectric fluid introduced into the air-tight container as changes in electrostatic capacitance corresponding to an angle of inclination, comprises:
variable capacitance means configured from a pair of variable capacitors constituted by the pair of differential electrodes and the common electrode connected in series across a power supply;
reference capacitance means constituted by a pair of reference capacitors connected in series across a power supply; and
differential amplifier means, in which a common connection point of the variable capacitors of the variable capacitance means serves as one differential input, and a common connection point of reference capacitors of the reference capacitor serves as another differential input.
According to feature (1), the electrostatic capacitances of each of the variable capacitors formed across the differential electrodes and the common electrode both exhibit maximum values in a horizontal state with no inclination regardless of individual differences. Zero-point adjustment to define the angle at which each capacitor exhibits a maximum value is therefore not necessary.
According to feature (2), the output signal of the differential amplifier means is proportional to a change in electrostatic capacitance xcex94C of the pair of variable capacitors formed across the pair of differential electrodes and common electrode of the electrostatic capacitance section. Temperature compensation is also not required because the temperature coefficient is nullified and there is no dependence on temperature.
Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.